The present invention relates to a nuclear medical diagnostic apparatus, both designed to detect, in one- or two-dimensional fashion, the radiation, such as gamma rays, emitted from the radio isotope (RI) administered to a subject, and to determine an RI distribution in the subject.
Nuclear medical diagnostic apparatuses are classified into a type which detects a single photon and another type which detects positrons. The first type generates an RI distribution by using a single photon (gamma ray) which single-photon type RI releases when it decays. The second type generates an RI distribution by using a pair of photons which are released when an IR positron annihilates.
The recent main medical diagnostic apparatus of single photon type is SPECT (Single Photon Emission Computed Tomography) apparatus. A wide line-up of SPECT apparatus is available at present, from one-detector type to four-detector type. Among the two-detector types developed is one in which the two detectors can take various positional relations, such as 180xc2x0 opposed arrangement and 90xc2x0-interval arrangement.
The one-detector type to the four-detector type best operate in different conditions. It is therefore desired that all these types be installed. This cannot be possible, however, because much cost and space are required.
The users have been strongly demanding for an apparatus that can perform the functions of the one-detector type to the four-detector type. The users have also been earnestly demanded for an apparatus that can be graded upward, first from one-detector type to two-detector type, then to three-detector type, and finally to four-detector type.
Conventional nuclear medical diagnostic apparatuses have some disadvantages, which will be described. FIG. 1A is a side view of a conventional nuclear medical diagnostic apparatus which has two radiation detectors. FIG. 1B is a front view of the apparatus as seen in the direction of arrow a shown in FIG. 1A. This conventional apparatus comprises a gantry 201, gantry rails 202, two Auger-type radiation detectors 203 and 204, arms 205a and 205b, a bed 206, and bed legs 207. The gantry 201 can move on the rails 202. The detectors 203 and 204 are arranged, opposing each other such that a patient may lie between them. The arms 205a and 205b are secured to the gantry 201 and hold the detectors 203 and 204, respectively. The bed 207 has a top plate 206a on which a patient may lie. The bed legs 207 support the bed 206.
The radiation detectors 203 and 204 weigh about 200 kg to 400 kg each. The total weight of the gantry 1 and the arms 205a and 205b holding the radiation detectors 203 and 204 is 1,500 kg to 2,000 kg. It is difficult to tilt the gantry 201, which is so heavy. Hence, the patient usually climbs onto the top plate 206a of the bed 206 as shown in FIGS. 1A and 1B, and images are formed after the patient is led into a dome 208.
In the medication examination using a conventional SPECT or PET apparatus, tomograms are formed while the patient is lying on the bed.
Positions the patient may take to obtain various tomograms are limited. A tomogram of the heart, for example, may be obtained by the use of a SPECT apparatus. If the arm overlaps the heart, it will absorb the radiation emitted from the apparatus. Consequently, the tomogram of the heart will be deteriorated. To prevent this, the patient on the top plate 206a shown in FIG. 1A must place his or her head on the right-end part of the plate 206a and both arms placed above his or her head. In this-position, neither arm overlaps the heart. (That is, neither arm is located between the heart and the radiation detector 203 or the radiation detector 204.) To remain in this position for a long time is very hard for the patient.
The top plate 206a on which the patient lies is thick and absorbs many gamma rays. Here rises the problem that the image obtained is deteriorated.
While the patient lies on the top plate, the liver and the heart are located close to each other. The radiation emanating from the liver adversely influences the tomogram of the heart, as is known in the art. Hence, it is very difficult to install an ergometer in order to carry out a stress test on the heart.
To acquire SPECT data from the head, the patient on the top plate 206a needs to place his or her head on the head rest (not shown) which is secured to the elevated part 206axe2x80x2 part, or a left part (FIG. 1A), of the top plate 206a. Then, the gantry 201 is moved until the radiation detectors 203 and 204 reach a position where the detectors can acquire data from the head. Once the radiation detectors 203 and 204 have been located near the head of the patient, the patient may likely to feel as if pressed or blocked. Inevitably the patient remains stressed during the acquisition of data. He or she can hardly be mentally relaxed and therefore cannot be tested for the function of his or her head.
To acquire mammo SPECT data or data representing still images of the breasts of a female patient, the radiation detector must be moved around the patient""s breasts. The positioning of the radiation detector is limited since the end of the effective view field of the detector is spaced from the outer surface thereof, by a distance of 40 mm or more. Practically it is impossible to move the radiation detector.
If the distance between the end of the effective view field of the radiation detector and the outer surface of the detector is short, the gantry cannot be tilted. Therefore, no data can be acquired from the breasts while the patient is lying on her stomach. It is impossible to position the patient so that mammo SPECT data may be acquired from the breasts.
With the conventional nuclear medical diagnostic apparatus having two radiation detectors, it is impossible to obtain still images of the patient in sitting position, by the simultaneous use of both radiation detectors. This is because each radiation detector is far larger than its effective view field, and also because much restriction is imposed on mechanical driving of the gantry. In most cases, one radiation detector is held extending outwardly at 90xc2x0, and only the other radiation detector is moved around the patient to detect radiation.
The first object of the present invention is to provide a nuclear medical diagnostic apparatus in which radiation detectors can be used in various numbers and the positional relation of the radiation detectors can be changed.
The second object of the invention is to provide a nuclear medical diagnostic apparatus which can acquire nuclear medical data about the various parts of a patient, such as the head and the heart, while the patient lies in a comfortable position.
In the present invention, a detector is provided inside a rotating ring. Therefore, the gantry can be made light. Further, the number and positional relation of detectors used can be appropriately changed.
In the present invention, the gantry can be swiveled and tilted, and the position and posture of the detector can be changed with a high degree of freedom. Thus, the position and posture of the detector can be changed so that a patient may take a comfortable position.
In the present invention, the gantry can be swiveled and the detector can be moved along the axis of a patient. The position and posture of the detector can therefore be changed with a high degree of freedom. Thus, the position and posture of the detector can be changed so that a patient may take a comfortable position.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentatlities and combinations particularly pointed out hereinafter.